The present invention relates to a door closer with a piston driven by a rack and pinion.
In a conventional door closer, the piston is moved to one side by the piston rod which simultaneously compresses a spring when the door opens. Such a spring is installed within the piston cylinder. The piston is returned to its original position by the force of the compressed spring, and accordingly, the door is closed.
As illustrated in FIG. 3, the contacting portion b of the last turn, out of all the spring turns having circular section, receives the force from the piston inner face. As shown in FIG. 4, when a force is transferred to the contacting portion b of spring a, the section of the contacting end portion b of spring a pushed by the inside face of the piston, becomes gradually thinner toward the end of the spring, and therefore the thicker section area receives more force than the thinner section portion. The portion surrounding line A--A (FIG. 3) of contacting portion b receives the most force, and accordingly the spring force is applied in an unbalanced, non-axial manner on the piston. Thus, during extended use, a certain friction occurs between cylinder inner wall and a region of the outside wall of the piston, causing wear, eventual leakage, piston wobbling and plugging of a communicating hole by eroded fragments. This situation will finally lead to faulty operation of the conventional door closer.
In U.S. Pat. No. 713,267, an actuator arm 37 axle drives a piston rod. Because the reference does not use a rack and pinion there is a significant moment tending to turn the piston rod about an axis perpendicular to the length of the rod. For this reason, the piston rod must extend through a return spring into a socket to prevent canting of the piston rod. See also U.S. Pat. No. 3,618,160. Other patents disclose either a rack and pinion mechanism, a spring, or both inside of a hydraulic chamber. See U.S. Pat. Nos. 1,595,723; 4,048,694; 4,073,033; 4,097,956; 4,234,996; 4,378,612; 4,660,250; and 4,847,946.